The present invention relates to a microwave data transmission apparatus which is adapted to transmit and receive information by microwave.
Conventionally, the construction shown in FIG. 7 is used as a microwave data transmission apparatus for transmitting and receiving information by microwave.
In FIG. 7, an identification tag 2 is adapted to answer with the fixed information stored therein through the microwave signal waves with respect to a interrogator 1 when the interrogator 1 asks a question through the microwave signal radio waves with respect to the identification tag 2. The interrogator has therein a signal generator 3 for generating the microwave signals, a transmitting antenna 4 for transmitting into the air as the waves the signals coming from the signal generator 3, a receiving antenna 5 for catching the waves fed from the identification tag 2, and a demodulator 6 for demodulating the microwaves coming from the receiving antenna 5. Also, the identification tag 2 has a receiving antenna 7 for catching the waves fed from the interrogator 1, a demodulator 9 for demodulating the microwaves caught by the receiving antenna 7, a signal generator 10 for generating the carrier waves of the microwave band, a code generator 11 for fixedly storing the code information to generate the code information signals in accordance with the outputs of the demodulator 9, a mixer 12 (which may be a modulator) for mixing the code information signals fed from the code generator 11 with the carrier-wave signals fed from the signal generator 10, and a transmitting antenna 8 for transmitting the output signals of the mixer 12.
In the conventional microwave data transmission apparatus of the above-described construction, the signals obtained from the signal generator 3 within the interrogator 1 are transmitted towards the identification tag 2 from the transmitting antenna 4. The transmission signals are received by the receiving antenna 7 of the identification tag 2 and continuously demodulated by the demodulator 9. The signal after the demodulation functions as a controlling signal for controlling the code generator 11 and the signal generator 10. The code information signals are fed into the mixer 12 from the code generator 11 by the control of the signals after the demodulation. Also, the carrier waves of the microwave band are fed into the mixer 12 from the signal generator 10. In the mixer 12, the carrier waves of the microwave band are modulated by the code information signal. The modulated signals are transmitted into the air as microwave signals towards the interrogator 1 by the transmitting antenna 8 of the identification tag 2. In the interrogator 1, the waves from the identification tag 2 are received by the receiving antenna 5, and the fixed information stored in advance in the identification tag 2 is fetched through demodulation by the demodulator 6.
However, as a signal generator 10 for reliably transmitting the carrier waves of the microwave band is necessary within the identification tag 2 in the above-described microwave data transmission apparatus, a power-supply apparatus of comparatively large capacity is provided for the driving operation of the signal generator 10. Thus, the construction of the identification tag 2 is rendered more complex and larger in size. Also, in the conventional apparatus, no consideration is given to changing the code information in the memory of the code generator 11, thus resulting in an extreme limitation in regard to flexibility and application.